MEPS 138:15-25 (1996) - doi:10.3354/meps138015

Onshore-offshore pattern and variability in distribution and abundance of bay anchovy Anchoa mitchilli eggs and larvae in Chesapeake Bay

MacGregor JM, Houde ED

The pattern and daily variability of kilometer scale, onshore-offshore distributions of bay anchovy Anchoa mitchilli eggs and larvae were determined from 4 d of repetitive sampling on a transect in mid-Chesapeake Bay. The 13 km transect ran from
nearshore to the most offshore area of the Bay, passing through a river-plume front. Most spawning by bay anchovy occurred offshore. Eggs and recently hatched larvae were 30 to 200 times more abundant offshore than at inshore and frontal stations. Few
eggs and larvae occurred below the pycnocline, where oxygen levels often were too low for survival or normal development. Mean larval lengths and relative (but not absolute) abundances of large (&GT=5.5 mm standard length) larvae increased in an offshore
to inshore direction. Apparent larval mortality rates, which were both size- and area-specific, were highest offshore and higher for small length classes. There was no indication that anchovy eggs or larvae were concentrated in the frontal region, but
gelatinous predators and zooplankton suitable as larval prey tended to increase at the front. While significant transport of larvae from offshore to inshore may occur, most larvae of all sizes were offshore, indicating that recruitment of anchovy is most
dependent on processes in the offshore region.